If you are not into gaming then you don't need 256 megs. 128 is more than enough for Photoshop, even 64 meg would do that job easily.
A 128 meg card such as a nVidia MX5200 is a reasonable spec card but won't keep up with the latest game.
If you prefer ATI, the 9200 series is about the nearest equivalent to the nVidia 5200.
Both the above cards can be bought very cheaply now, under Â£30 (GB pounds) in many places.